PS One (PM-41 board) has a short circuit at 3v after changing modchip

[Fien]

My PS One (PAL, SCPH-102) had 2 modchips in it. A MM3 for booting and ONEchip for BIOS patching. Because back then with only the ONEchip it read discs bad. But today I tried to place the ONEchip on another place after I saw a video.

I first removed both modchips. At that point the short on 3v was not there. Then I re-installed the ONEchip in it's new place and powered the console on. The power LED flashes short and then turned off. I immediately though maybe it was a short on the 3v so I checked it with the multimeter... 0 Ohm between 3v and ground.

But I can't find where the short is. I removed the ONEchip and bathed/brushed the board in alcohol, hoping to remove maybe a loose mini splash of solder somewhere on the board. But the short is still there. I checked every point I touched with soldering and can't see any shorts.

I know the solder pad of C705 is damaged because there was a big through-hole capacitor soldered on it which was removed about 10 times. But that can be fixed after the 3v short is removed.

The jumper wire of the NTSC color fix was already there before I touched it today, so it won't be the cause of the short.

Left is after the ONEchip install, right is the board after removing the chip and cleaning.

 

[Hayato213]

You can check with continuity mode, if you get a beep sound then it indicate a short circuit.

 

[Fien]

I did that and it beeps/gives 0 Ohms. That's why I know there's a short. But I don't know where the short is... how to find that?

 

[Hayato213]

I would check your soldering, poor soldering can lead to a short circuit.

 

[Fien]

In the OP I already wrote I removed the modchip. So all the soldering I've done is removed.

 

[Hayato213]

You would have to find where on your board is causing the short circuit, if you got thermal imagine camera you can use the injecting voltage method.

 

[Fien]

Unfortunately I don't have thermal imaging equipment or a variable power supply available

 

[Fien]

I found the short... it's really a tiny drop of solder which has fallen on a random place on the board, touching the legs of a IC. Not even near the places I soldered on.

The board still can't be tested, because the fuse PS606 is blown. According to the service manual it's a "LINK, IC (CCP2E20) 0.8A". Seems like a 0,8A fuse in miniature format. Don't know where to find it at the moment, on Aliexpress they only have 2A.

 

[Fien]

This board is repaired. I ordered a fuse from eBay and after soldering it into place, the board works fine.

It still needs two modchips. The ONEchip for BIOS patching and the MM3 for booting. The ONEchip can do the booting too, but somehow it degrades the disc reading performance much more then the MM3.

 

[master801]

This board is repaired. I ordered a fuse from eBay and after soldering it into place, the board works fine.

It still needs two modchips. The ONEchip for BIOS patching and the MM3 for booting. The ONEchip can do the booting too, but somehow it degrades the disc reading performance much more then the MM3.

Why not use a PsNee?

 

[Fien]

On a PAL PS One it needs a whole Arduino board which is more difficult to fit into the case. And back then I could get the PIC's cheap and I already had a Willem Programmer to program them.

Does the PsNee not affecting the disc reading performance like some PIC modchips?

 

[Armadillo]

Does the PsNee not affecting the disc reading performance like some PIC modchips?

Yes and no.

You get degraded performance during the initial disc check, but once it's passed performance should be the same as without the chip. Degraded performance as far as I know is caused by a bug in the pic chips, they don't let go of where they inject the scex code.

https://www. reddit.com/r/psx/comments/1avdxt7/what_kind_of_modchip_is_that/krf2m4b/ (remove the space, gbatemp keeps turning reddit links into media for some reason).

"The later chips mitigated this by replacing the link with a switch inside the firmware - this turned off the constant signal that was being fed into the tracking servo when it was not needed, which improved the tracking performance - unfortunately, Mayumi 4.0 had a bug in it that resulted in the output being left asserted at the end of SCEx injection and since things like MM3 and OneChip appear to have been copied from Mayumi4.0 they have it too.

The reason I consider the PSnee to be the best in this case is that it's much less intrusive - it still uses the same internal gating of the WFCK signal but once it's done it leaves the outputs floating and doesn't further interfere with the servo operation. Since the lead-in (and hence the SCEx data) is always read at 1x speed where there is more gain margin in the tracking servo and that's the only time the outputs are active the performance is very close to what you get without a chip installed at all."

You can actually hear it on a lot of the pm-41 (2) boards (last revision of psone), soon as the signal is dragged down there is a chirping noise from the laser, Psnee the chirp is only there on the disc check, once it's done the noise goes, older chips, effected boards will chirp all the time.

There was a topic here https://www.obscuregamers.com/threads/psone-pm-41-2-a-modchip-problem.618/post-3771.html discussing that noise on the pm-41 (2) and the creator mentioning the bug on the pic chips (post #40) as well.

"I think one classic modchip had some kind of bug that would have it permanently drag down the TEI signal after injection.
This bug could explain the chirping."

If you go the psnee way , there is actually a newer psnee based on the original now
https://www.psxdev.net/forum/viewtopic.php?f=47&t=3854

That does the bios patching a different way so the console doesn't get forced to 60HZ on boot when bypassing the region check.

I've never used that one though, only the original.

 

[Fien]

Yes and no.

You get degraded performance during the initial disc check, but once it's passed performance should be the same as without the chip. Degraded performance as far as I know is caused by a bug in the pic chips, they don't let go of where they inject the scex code.

Maybe that's why a lot of discs are just not recognised when using the ONEchip for booting, but boots fine with the MM3.

It's degraded when it needs to recognize the disc.

If you go the psnee way , there is actually a newer psnee based on the original now
https://www.psxdev.net/forum/viewtopic.php?f=47&t=3854

That does the bios patching a different way so the console doesn't get forced to 60HZ on boot when bypassing the region check.

I've never used that one though, only the original.

This sounds interesting.

But somewhere I read it has a bug making the CD player and memory card manager not working?

Also it has not a lot of information about how to program a Arduino Nano for it. Only saying not to use the USB or COM for it.

I have a Willem Programmer to write PIC's and EPROM's, but have no experience with Arduino boards.

 

[SylverReZ]

I found the short... it's really a tiny drop of solder which has fallen on a random place on the board, touching the legs of a IC. Not even near the places I soldered on.

The board still can't be tested, because the fuse PS606 is blown. According to the service manual it's a "LINK, IC (CCP2E20) 0.8A". Seems like a 0,8A fuse in miniature format. Don't know where to find it at the moment, on Aliexpress they only have 2A.

Use some desoldering braid to remove the bridge, a microscope is also recommended to get a better look at your work.